Morning Sickness (Vomiting During Pregnancy) Overview

While you are pregnant, nausea and vomiting are common. A majority of women get mild to moderate symptoms during the first three months (first trimester) of
pregnancy. These symptoms are usually gone by the fourth month.

Although this condition is often called morning sickness, most women have symptoms throughout the day.

Very rarely, a pregnant woman may experience a more serious condition involving severe vomiting, dehydration, and weight loss. This is called hyperemesis gravidarum.

Vomiting During Pregnancy Causes

The exact cause of nausea and vomiting in pregnancy is not clear. Most evidence points to rapid changes in hormone levels. These fluctuations may cause changes in the muscle contraction and relaxation patterns of your stomach and intestines, thus leading to nausea and vomiting.

The hormones that seem to have the most to do with this process include the pregnancy hormone
human chorionic gonadotropin (hCG), estrogen, and progesterone. Abnormal levels of thyroid hormones have also been reported in women with severe vomiting, although a cause-and-effect relationship remains unclear. Some studies have shown that nausea is worse when your blood sugar level is low. Some researchers have found that women who are more likely to have nausea from
birth control pills,
migraines, or motion sickness are at higher risk for nausea and vomiting in pregnancy.

If you have a family history of hyperemesis gravidarum, you are more likely to have the condition. What causes hyperemesis gravidarum remains unknown despite active research.

The more popular theories fall into three areas:

Hormonal: Elevated levels of human chorionic gonadotropin (hCG) or a component of this hormone may play a role in inducing vomiting. Thyrotoxicosis or hyperthyroidism is also believed to be associated with the condition. Another hormone thought to be involved is serotonin. Serotonin is a brain chemical that affects both the central nervous system and the gastrointestinal (GI) tract. These effects are believed to induce vomiting. During pregnancy, the upper GI tract may slow down and thus contribute to increased nausea and vomiting. Several studies have shown that this slowdown in the GI tract is increased in pregnant women with severe vomiting.

Gastrointestinal:Helicobacter pylori bacteria that live in the intestinal tract may cause the development of peptic ulcer disease. These bacteria are found in a greater percentage among pregnant women and greater still in women with hyperemesis gravidarum. Antibiotics are used to treat all of these conditions.

Psychosocial: Although the idea is controversial, some researchers think the condition may be a woman's psychological reaction against the pregnancy and might arise from conflict within the family and her home environment. In these cases, counseling is recommended.